The goal of this proposal is to examine the development of complex auditory information processing in infants. Two sets of experiments are planned: one dealing with the perception of rhythmic structure and the other with the perception of speech sounds. The first set of experiments is intended to delineate the precise conditions that give rise to rhythm discrimination and the formation of rhythmic categories and to test competing hypotheses about how rhythm is perceptually organized. In the second set of experiments, we will study speech sound discrimination and category formation. A main issue here is whether, and at what age, infants display the same kinds of phonetic trading relations and context effects as are found for adults. In addition, both sets of experiments are designed to test, in the auditory domain, a developmental theory of information processing that is based on earlier work on infant visual perception. In all experiments we will use a visual habituation procedure to assess auditory discrimination and categorization. The principal advantage of this procedure over other techniques is that it is suitable for a wide range of age groups, and it will therefore enable us to monitor developmental changes in auditory information processing.